Abstract: The excavation of 16,000,000 yd³ of rock at LG-2, part of the La Grande hydropower project in Canada, has been completed. The world's largest underground powerhouse, with a capacity of 5328 megawatts, will be constructed in a 3,700,000 yd³ rock excavation there. Rather than design for the worst case, and apply unnecessarily high safety factors throughout the project, the excavation was planned for the best case, with problems treated individually. This approach was successful because of unusually close field control by a full-time geotechnical team. Considerable rock excavation and concrete construction were eliminated by controlled blasting of rock pillars at the intake and of rock shoulders in the machine hall. Delays and overruns were neglible.